Field of the Invention
The invention generally relates to projection screen, in particular, to a projection screen suitable for use in ultra-short focus projection system.
Description of Related Art
As to the ultra-short focus projection system, it needs to project a large size image in a very short projection distance, and therefore the range of the incident angle for the image beam used in projection is relatively greater than that in the common situation. If the common projection screen is used, it would cause the issue that the luminance gain is insufficient or the luminance distribution on the screen is not uniform. As an example in case, the projection screen used in long focus projector is taken as the projection screen used in ultra-short focus projector. Only a relatively small range of the incident angle of the image beam is considered in design for the projection screen used in the long focus projector. If the projection screen used in long focus projector is taken as the projection screen n ultra-short focus projection system, the reflected image beam would deviate from the viewing direction of viewer when the image beam is incident on the projection screen at a relatively large incident angle. As a result, it causes the issues that the luminance gain is insufficient and the luminance distribution on the screen is not uniform.
On the other hand, in case, the projection screen with large viewing angle is applied to the ultra-short focus projection system. Since the projection screen with large viewing angle has a light-scattering layer, the image beam in any incident angle can be uniformly reflected and it can solve the issue that the luminance distribution is not uniform. However, the drawback of this manner is that the luminance gain is not high. Further, if the projection screen with high luminance gain is applied to the ultra-short projection system, the viewer would see the projection image with uneven luminance when viewing in different viewing angles.
Further, if the projection screen with high contrast is applied to the ultra-short projection system, the projection screen with high contrast has light absorbing material and the absorbing material with respect to the light only has the selection n incident direction. In other words, when the propagation direction of the image beam is close to the propagation direction of the ambient light, the light absorbing material would absorb both the image beam and the ambient light. This manner would also reduce the luminance gain. In other words, this manner scarifies the luminance gain to reach high contrast level without the advantage having both high luminance gain and high contrast.
In addition, if the projection screen with capability of anti-ambient light is applied to the ultra-short projection system, the reflectivity of the projection screen with capability of anti-ambient light has selectivity to the incident angle of light, and the image beam within a specific range of the incident angle can be reflected back to the viewer and the ambient light at the other incident direction would be absorbed or deviated from the viewing direction. However, if the projection screen with capability of anti-ambient light is applied to the ultra-short projection system, it is difficult in design to reach the advantages having high gain, wide viewing angle, and high contrast.
As to the foregoing descriptions, how to solve the foresaid issues is essentially concerned by the one for development.
The section of “description of related art” is just used to help the understanding of the invention, the disclosure in the section of “description of related art” may comprise some prior art not known by the one with ordinary skill in the art. The disclosure in the section of “description of related art” does not represent all the issues to be solved by this section or by one or more embodiments in the invention and already known or recognized by the one with ordinary skill in the art before the application of the invention.